2 use rustc::ty::{TypeAndMut, TyRef};
4 use utils::{in_external_macro, span_lint};
6 /// **What it does:** This lint checks for instances of `mut mut` references.
8 /// **Why is this bad?** Multiple `mut`s don't add anything meaningful to the source.
10 /// **Known problems:** None
12 /// **Example:** `let x = &mut &mut y;`
16 "usage of double-mut refs, e.g. `&mut &mut ...` (either copy'n'paste error, \
17 or shows a fundamental misunderstanding of references)"
23 impl LintPass for MutMut {
24 fn get_lints(&self) -> LintArray {
29 impl LateLintPass for MutMut {
30 fn check_expr(&mut self, cx: &LateContext, expr: &Expr) {
31 if in_external_macro(cx, expr.span) {
35 if let ExprAddrOf(MutMutable, ref e) = expr.node {
36 if let ExprAddrOf(MutMutable, _) = e.node {
40 "generally you want to avoid `&mut &mut _` if possible");
42 if let TyRef(_, TypeAndMut { mutbl: MutMutable, .. }) = cx.tcx.expr_ty(e).sty {
46 "this expression mutably borrows a mutable reference. Consider reborrowing");
52 fn check_ty(&mut self, cx: &LateContext, ty: &Ty) {
53 if let TyRptr(_, MutTy { ty: ref pty, mutbl: MutMutable }) = ty.node {
54 if let TyRptr(_, MutTy { mutbl: MutMutable, .. }) = pty.node {
55 span_lint(cx, MUT_MUT, ty.span, "generally you want to avoid `&mut &mut _` if possible");